Gas can/ pump accuracy?

3D
Profile picture for user 3D
Posts
938
Joined
5/1/2008
Location
Tamaqua, PA US
3D
Almost every week I have to fill 5 five gallon plastic gas cans with ethanol free gas for a weekend at the races between the bikes, generator, and pit cruiser. My question is, why does the pump always say 27.5 to 28 gallons? I fill them to exactly the 5 gallon mark on the can. I understand that weather can affect the size of the can and volume of the gas itself, but that much? It makes me feel like I should be adding oil to the 2 stroke can, but not if the pump is what's inaccurate. Which do you think is inaccurate? Pump or cans? Maybe both?
2
|
sandtrack315
Profile picture for user sandtrack315
Posts
2550
Joined
7/19/2013
Location
Philadelphia, PA US
sandtrack315 10/9/2020 5:48am
10/9/2020 5:48am
A guess, but probably the cans. If the pump was off, they'd be losing money, and I guarantee they are not in the business of losing money. Are you using different gas stations? If so, then it's def the cans.

Get a gallon jug and fill up the can 5 times. Then mark where the water is at. Now you know.
2
3D
Profile picture for user 3D
Posts
938
Joined
5/1/2008
Location
Tamaqua, PA US
3D 10/9/2020 6:01am
10/9/2020 6:01am
They're not losing money. It should only be 25 gallons, not 28.
1
GoggleFiend904 10/9/2020 6:07am
10/9/2020 6:07am
Cans. Mine are accurate when they are new, over time the can warps. I made my own marks a couple years ago after the can warped and they have stayed accurate. Always trust the pump, I imagine they are heavily regulated. Especially in CA
3
c0ncEpT
Profile picture for user c0ncEpT
Posts
1269
Joined
5/13/2015
Location
Harrison Twp., MI US
c0ncEpT 10/9/2020 6:11am
10/9/2020 6:11am Edited Date/Time 10/9/2020 6:14am
The variance is in the cans. The pumps are are flowed, sealed, and certified by the department of weights and measures.
6

The Shop

See All »
ElliotB16
Profile picture for user ElliotB16
Posts
1059
Joined
6/10/2019
Location
Cairo, GA US
ElliotB16 10/9/2020 6:14am
10/9/2020 6:14am
I’ve noticed this too. Pump says 5 gallons but can only shows 4.5
mxtech1
Profile picture for user mxtech1
Posts
1957
Joined
7/21/2011
Location
Galesburg, IL US
mxtech1 10/9/2020 6:30am
10/9/2020 6:30am Edited Date/Time 10/9/2020 7:01am
They are accurate. The only pump "loss" is that first little bit that trickles out from the prior use before the pump kicks on, maybe a few ounces at most.

You might want to verify that your markings on your 5 gallon cans are accurate. It would seem to me you are putting about 2 to 2.5 extra quarts of fuel into each can. That would take a 32:1 ratio down to 35.5:1 (11% reduction)

A gallon of gas weighs 6.3 lbs. Take a bathroom scale with you next time you go to the pump. Set the empty 5 gallon container on the scale and tare it. Pump until you have 31.5 lbs of fuel on the can, check against the mark. I would do this for each can to see if they are accurate. I think you will find you get to 31.5 lbs of fuel a little bit before each line. This might seem silly, but you could do it once and then have piece of mind going forward.

The 1/2 gallon variance you see each time is showing how accurate you are at shutting the pump off at the line each time. 1/2 gallon variance over 25 gallons would impact the oil ratio by about 1% , its only ~ 2.5 ounces per can.

But keep in mind the 2.5 ounce variance per can is in addition to the already extra 2 - 2.5 quarts, so your total impact to oil ratio could be as high as a 12% reduction.
3
1
3D
Profile picture for user 3D
Posts
938
Joined
5/1/2008
Location
Tamaqua, PA US
3D 10/9/2020 7:28am
10/9/2020 7:28am
mxtech1 wrote:
They are accurate. The only pump "loss" is that first little bit that trickles out from the prior use before the pump kicks on, maybe a...
They are accurate. The only pump "loss" is that first little bit that trickles out from the prior use before the pump kicks on, maybe a few ounces at most.

You might want to verify that your markings on your 5 gallon cans are accurate. It would seem to me you are putting about 2 to 2.5 extra quarts of fuel into each can. That would take a 32:1 ratio down to 35.5:1 (11% reduction)

A gallon of gas weighs 6.3 lbs. Take a bathroom scale with you next time you go to the pump. Set the empty 5 gallon container on the scale and tare it. Pump until you have 31.5 lbs of fuel on the can, check against the mark. I would do this for each can to see if they are accurate. I think you will find you get to 31.5 lbs of fuel a little bit before each line. This might seem silly, but you could do it once and then have piece of mind going forward.

The 1/2 gallon variance you see each time is showing how accurate you are at shutting the pump off at the line each time. 1/2 gallon variance over 25 gallons would impact the oil ratio by about 1% , its only ~ 2.5 ounces per can.

But keep in mind the 2.5 ounce variance per can is in addition to the already extra 2 - 2.5 quarts, so your total impact to oil ratio could be as high as a 12% reduction.
I just weighed my fuel and it is 33 pounds. So I have a half pound more fuel when I go by the marks on the can. Thank you. I'll be trusting the pump from here out. My younger son is a top level super mini racer. I can't afford to lack oil. I already lost one crank this season.
1
Bruce372
Profile picture for user Bruce372
Posts
6341
Joined
4/1/2008
Location
US
Bruce372 10/9/2020 7:55am
10/9/2020 7:55am
Serious fines if the pump is off and they do check and certify that stuff
2
SEE ARE125
Profile picture for user SEE ARE125
Posts
5574
Joined
3/28/2012
Location
TN US
SEE ARE125 10/9/2020 7:59am
10/9/2020 7:59am
If you look on the pump there will be an inspection sticker and it’ll have the date of last inspection. They are inspected regularly for accuracy.
2
misterwaterfallin 10/9/2020 8:10am
10/9/2020 8:10am
SEE ARE125 wrote:
If you look on the pump there will be an inspection sticker and it’ll have the date of last inspection. They are inspected regularly for accuracy.
Most are years ago, it's uncommon to see one within the last 12 months at least around here. Also, gas changes volume and weight depending on the temp, so a more accurate scale would be weight but that's impractical so you have to deal with some margin of error
LKHill
Profile picture for user LKHill
Posts
853
Joined
9/8/2020
Location
NY US
LKHill 10/9/2020 8:30am
10/9/2020 8:30am Edited Date/Time 10/9/2020 8:31am
Ha, Ha, the old flim, flam gas pump scam. They do dial back the pumps but it's not very often you will run across it. In this case they dialed it up? Just margin of error more than likely. Most cans need to hold more than their rated amount to allow for expansion.
2
Falcon
Profile picture for user Falcon
Posts
10111
Joined
11/16/2011
Location
Menifee, CA US
Fantasy
798th
Falcon 10/9/2020 8:33am
10/9/2020 8:33am
c0ncEpT wrote:
The variance is in the cans. The pumps are are flowed, sealed, and certified by the department of weights and measures.
This. Notice how the pump reads in tenths, hundredths, and thousandths of a gallon? It has to be that accurate. You could be off by several hundredths (maybe even tenths) just by your eyeballs alone on the can markings.
loftyair
Profile picture for user loftyair
Posts
2769
Joined
7/3/2009
Location
riverside, CA US
loftyair 10/9/2020 8:36am
10/9/2020 8:36am
Yep, pumps more accurate. I 'marked' my own containers to signal truth.
MxKing809
Profile picture for user MxKing809
Posts
6380
Joined
10/13/2013
Location
Big Sand Whoops, MI US
Fantasy
315th
MxKing809 10/9/2020 8:52am
10/9/2020 8:52am
People have gone off the gallon marks on the sides of that cans? The same vans that sell for $20 bucks and are mass produced over seas?

...... you guys trust those marks over pump readouts?
1

Post a reply to: Gas can/ pump accuracy?